Biomass contains carbohydrates or sugars (i.e., hexoses and pentoses) that can be converted into value added products. Production of biomass-derived products for non-food uses is a growing industry. Bio-based fuels are an example of an application with growing interest. Another application of interest is the use of biomass as feedstock for synthesis of various industrial chemicals from renewable hydrocarbon sources.
In recent years, an increasing effort has been devoted to find ways to utilize biomass as feedstock for the production of organic chemicals because of its abundance, renewability, and worldwide distribution. When considering possible downstream chemical processing technologies, the conversion of sugars to value-added chemicals is very important. Recently, the production of furan derivatives from sugars has become exciting in chemistry and in catalysis studies, because it aids one of the major routes for achieving sustainable energy supply and chemicals production. As illustrated in FIG. 1, which shows a schematic representation of a process for converting biomass into useful end products, furanic intermediates: 5-hydroxymethylfurfural (5-HMF), 2,5-furan-dicarboxylic acid (2,5-FDCA) and 2,5-dimethylfuran (2,5-DMF) have been called the “sleeping giants” of renewable intermediate chemicals. These intermediates are green building blocks for a range of materials, chemicals and fuels. As building blocks that have been much studied, and have enormous potential for use in the production of green plastics and chemicals, the U.S. Department of Energy has recognized furanic intermediates as one of the top high-potential green building blocks. 5-HMF is a dehydration product of hexoses and a potential substitute of petroleum-based building blocks of various polymers. 2,5-FDCA is derived from oxidative dehydration of hexoses and is considered as one of the top 12 compounds made from a sugar into a value-added chemical. 2,5-DMF is produced through hydrogenation of HMF and is less volatile and of 40% higher energy density than ethanol. (See generally, T. Werpy, G. Petersen, TOP VALUE ADDED CHEMICALS FROM BIOMASS: Vol. I—Results of Screening for Potential Candidates from Sugars and Synthesis Gas, August 2004. (Available electronically at http://www.osti.gov/bridge))
Even though much interest has arisen to develop better ways of making building blocks for the emerging market of green materials and renewable energy, until recently, furanics have not been commercialized because large-scale production of furanic intermediates have not been cost-effective. Various different processes have been advanced for the catalytic conversion of sugar to furan chemicals. (See generally, X. Tong et al., “Biomass into Chemicals: Conversion of Sugars to Furan Derivatives by Catalytic Processes,” APPLIED CATALYSIS A: GENERAL 385 (2010) 1-13.)
Of the furanic intermediates, furan-dicarboxylic acid (FDCA) is a commercially valuable material that can used as a precursor for various plasticizers, or a replacement for purified terephthalic acid (PTA), or other value added products. Over the years, chemical manufacturers have sought a simpler way of producing and manipulating FDCA, given the known problems associated with working with FDCA, such as its poor solubility in common organic solvents and being soluble in high boiling solvents like DMSO. Another problem that arises when using FDCA in melt polymerization is the tendency for the FDCA molecule to decompose at temperatures greater than about 180° C. to furoic acid, leading to poor product quality. All of these challenges can be solved by derivatizing FDCA into an ester. Current acid catalyzed esterification, however, typically requires about 20 hours or more to produce diester molecules. Such a process takes too long and is not cost effective for high-volume, mass production of the esters. Furthermore, purification of the resulting esters requires washing with base to remove residual acid catalyst that may affect the quality of the FDCA esters in downstream processing. Other alternatives for esterification of FDCA require its activation as a diacyl chloride, which makes the process not sustainable or economical.
The preparation of an acyl chloride (i.e., COCl moiety) requires treating an acid with thionyl chloride in stoichiometric amount and then converting it to an ester. Safety concerns arise when using thionyl chloride on a large scale, as the byproducts for the acylation reaction are SO2 and HCl, and HCl for the esterification. The SO2 and HCl are captured with a weak base and then disposed as waste. Moreover, conversion of FDCA to the corresponding furan-2,5-dicarbonyl dichloride would generate a mixture of side products upon esterification with alcohols because of unstable intermediates. Additionally, the acyl chloride is sensitive to water and would require special storage conditions.
WO 2011/023590 A1 by Grass et al. describes, in part, methods for producing mixtures of ester derivatives of 2,5-furan dicarboxylic acid (FDCA) and the use of the derivative material (isononyl furan dicarboxylate) as plasticizers. In particular, the disclosure relates a method using an acid or metal catalyst for preparing esters of FDCA with isomeric C-9 alcohols, in particular mixtures of linear and branched nonanols (e.g., isononyl furan-2,5-dicarboxylate). The method follows largely a conventional process of esterification. According to Grass et al., one can prepare an ester using either FDCA or a reactive derivative such as the corresponding dichloride with a strong mineral acid. Further, the method unfortunately experiences certain disadvantages, such as: FDCA at temperatures above 190° C. tends to eliminate CO2, and forms monocarboxylic acids (e.g., furoic acid), which cannot be converted to the desired product, and to avoid the formation of color and decomposition of FDCA at the reaction temperatures one may need to use dimethyl furan dicarboxylate as a precursor.
In view of such issues of converting or synthesizing esters of FDCA according to current techniques, a need exists for a simple, clean, and economic process for converting carbohydrates into building blocks for materials and fuels for commercialized use.